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Why were the small temperature fluctuations found by COBE important?

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Oval map of the cosmic microwave background radiation from NASA's WMAP mission, showing a mottled pattern of blue, green, yellow, and red representing temperature variations. — Cosmic microwave background A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.

The small temperature fluctuations detected by the Cosmic Background Explorer (COBE) were fundamentally important because they provided the first evidence of departures from exact isotropy in the cosmic microwave background.1

While the radiation field is uniform to one part in 100,000, these tiny "wrinkles" or fluctuations indicated that the early universe was slightly denser in some regions than in others. Theoretical cosmologists had long predicted that such variations were necessary for gravitational separation to occur. These density differences acted as the seeds that allowed matter to condense, ultimately leading to the formation of galaxies and clusters of galaxies from an otherwise structureless universe. By confirming these fluctuations, COBE provided critical observational support for the big bang theory of the universe's origin.21